The radio range at Pali-Vanyi resembled to a great extent the radio ranges used for centuries before by the Federal airways of the United States of America, Earth. The increasing use of ultra-high frequency waves had made obsolete the four towers of the intermediate frequency range. Small, compact, the new range system had through the long decades of scientific advancement after the war years of the 20th century reached a stage of efficiency a hundredfold greater than its predecessor. A small antenna array atop the broadcast station consisting of four vertical radiators mounted at the terminals of a horizontal X replaced the towers of yesteryear. The four bars of the X pointed northeast, northwest, southwest and southeast. The NW and SE radiators sent out a steady N (dash-dot) in Morse code, the SW and NE a steady A (dot-dash). At thirty second intervals the identification letters of Pali-Vanyi [dot-dash-dash-dot dot-dot-dot-dash] were transmitted from all radiators. A ship coming in from the west, directly on course, heard both N and A simultaneously and with equal strength so that they interlocked and formed a steady dash. A swerve to the north of the course meant that the N signal would be predominant in the ship's receiver; to the south, that the A would be predominant. Rotating the goniometer counter-clockwise would so change the radio frequency in the four signal radiators as to cause all on-course signals to swing similarly, and ships on the beam would follow it blindly around, especially when their compasses were put awry by natural causes. A 90 degrees swing would completely reverse the so-called N and A quadrants; hence the beam would completely lie. WHAT would the destroyer's speed be? Probably twelve or fourteen hundred m.p.h. Twenty minutes or less to swing the beam. With one hand Silvy Ward began to rotate the goniometer, casting an eye at a nearby chronometer. Ninety degrees, say, in eighteen minutes. Five degrees per minute. Easy now! With a free hand Ward reached out and snapped on the shortwave transceiver which was used in communications when testing experimental equipment. He picked up the microphone and called: "Portiz, are you in position?" "Yes, sir!" the answer came promptly. "Directions, pal. Cut in the glide path transmitter now and stick with it until further instructions so that nothing goes wrong." "Yes, sir. But what's the idea, Silvy?" "No time to explain now, Portiz! I've work to do!" Ward snapped off, and immediately reached out for the televisorphone. He dialed Public Service and asked for his good friend Duka Dwane, Venusian utility magnate. "Duka," he barked after credentialling his way past a Mr. Dwane's-in-conference operator, "this is Silvy Ward of the Authority. There's a Martian destroyer coming in with obvious intentions of bombing Pali. I want you to black out the city immediately."